In the first nine months of 2012, the various models of the Prius from Toyota Motor Corp. (NYSE: TM) sold 46,380 vehicles in California to become the best selling car in the country's largest market for new cars. California accounts for about 11% of all U.S. new car sales, and 1.25 million new cars were purchased in the state during the first nine months of 2012.

As a percentage of total new car sales, the Toyota Prius accounts for about 3.7% of California purchases. If the Prius sold at the same rate in the rest of the U.S., it would account for about 403,300 of the 10.9 million new cars sold in the first nine months of this year. According to data from hybridcars.com, Prius models have sold nearly 210,000 units in the U.S. through September 2012, or about 65% of the 322,516 hybrids sold in the country.

The all-electric vehicles such as the Chevy Volt from General Motors Co. (NYSE: GM), Tesla Motors Inc. (NASDAQ: TSLA), Toyota, and others have sold a total of 31,114 in the U.S. during the first nine months of the year.

The Prius has plenty of headroom to grow U.S. sales and just counting the growth in sales of the Prius liftback model, up 25.8% year to date compared with the first nine months of 2011, in five years the company could be selling as many as 1.2 million hybrids annually in the U.S. While it's hard to predict how many cars will be sold in the U.S. in 2017, the highest number ever sold in the U.S. was about 17 million, so using that figure as a base, the Prius could nearly double its share of total U.S. car sales to 7%.

The best-selling vehicles in the U.S. right now are the F series trucks from Ford Motor Co. (NYSE: F), which sold just over 310,000 vehicles in the first six months of 2012. Extrapolating to include the third quarter, the popular pickup trucks have outsold the Prius by more than 2 to 1. But sales are growing at just over half the rate of Prius sales, and with gasoline prices on a long-term climbing trend, it's not a big stretch to imagine that the Prius line will be outselling the F series trucks sometime within the next five years. That would really be something.